Which term describes a chromosomal abnormality with an extra chromosome?

The term that describes a chromosomal abnormality involving an extra chromosome is trisomy. Trisomy occurs when an individual has three copies of a specific chromosome instead of the usual two. This can lead to various genetic disorders, the most well-known being Down syndrome, which is caused by an extra copy of chromosome 21.

Monosomy refers to the absence of one chromosome from a pair, which is not relevant in this context since we are discussing an additional chromosome. Euploidy refers to the complete sets of chromosomes, typically a multiple of the haploid number, focusing more on the overall set configuration rather than individual anomalies. Polyploidy is a condition where an organism has more than two complete sets of chromosomes, which is a broader categorization and does not specifically address the presence of a single extra chromosome. Thus, trisomy is the most accurate term to describe this specific chromosomal abnormality.